1. Field of the Invention
The present invention generally relates to a PLC (Planar Light-wave Circuit) module, and in particular, to a PLC module with a heat transfer device that is capable of maintaining the temperature distribution of a PLC uniform, while increasing the heat efficiency therein.
2. Description of the Related Art
A slight variation in the temperature of the PLC changes the refractive index within a light waveguide, thus changing the wavelength characteristics and the optical power of the PLC. Thus, a uniform temperature distribution across the PLC is essential in the field of optical communications. To this end, the overall temperature of the PLC is maintained uniformly by transferring the heat to the PLC. Accordingly, an efficient heat transfer mechanism is important from a heat source to a PLC. A known apparatus in this art is a planar WDM (Wavelength Division Multiplexing) device with a phase array configuration that is capable of utilizing light interference between the light waveguides with different light paths. This type of planar WDM device is typically packaged with a thermal management system, such as Peltier devices. However, the thermal management system used in the prior art has some drawbacks in that it is highly costly and consumes a lot of power to operate as it requires heat exchange with its surroundings.
To address the prior art problem, an improved thermal management system for a PLC module 10 is provided as shown in FIG. 1. The PLC module 10 is assembled as a single optical device that is capable of transferring the heat to the PLC module. The PLC module 10 is comprised of a PLC 11, a heat transfer plate 12 attached under the PLC 11, a heat sensor (not shown) between the PLC 11 and the heat transfer plate 12, and a heat emitting plate 13 under the heat transfer plate 12.
The PLC 11 is designed to divide the intensity of an optical signal according to the shape of a core, which is formed by depositing a plurality of silica or thin polymer films on a silicon or quartz substrate. As readily apparent to those skilled in the art, the signal intensity is produced based on the difference between the refractive indexes of a core and a clad surrounding the core.
The heat emitting plate 13 is provided with a heating line 14 formed by a strand of resistance wire that is bent in a zigzag shape. Both ends of the heating line 14 are connected to the external electric lines 18 to generate heat for the PLC 11.
The PLC module 10, as described in the preceding paragraphs, transfers heat generated from the heating line 14 to the PLC 11 through the heat transfer plate 12. Meanwhile, the temperature of the heat transfer plate 12 is monitored and controlled via the heat sensor.
However, in the course of transferring heat from the heat emitting plate 13 to the PLC 11, the heat transfer plate 12 experiences heat loss, thereby decreasing the heat efficiency and making the temperature distribution of the PLC 11 non-uniform. As a result, the PLC 11 undergoes changes in its characteristic wavelength and causes loss in its optical power. Moreover, as the heat is transferred through the heat transfer plate 12, the time required for the PLC module 10 to reach the normal operation temperature is undesirably long.
The present invention is directed to provide a PLC module in which the heat generated from a heat source is transferred to a PLC efficiently in order to maintain uniformity in the temperature distribution of the PLC.
According to an aspect of the invention, the inventive PLC module is capable of reaching the normal operation temperature much more quickly than the prior art module.
According to another aspect of the invention, a heating line is directly attached to the lower surface of a PLC by a silk printing process, and an insulation layer is coated on the lower surface of the PLC with the heating line fixed thereto. In addition, pads are attached to both ends of the heating line to connect the heating line to an electric line.
According to another aspect of the invention, a method of making a semiconductor device is provided. The method includes the steps of: providing a planar lightwave circuit (PLC); adhering a heat line to the lower surface of the PLC; providing an insulation layer attached to the lower surface of the PLC containing the heat line; and, coupling an external power source coupled to the heating line for generating heat thereto. The heat line is adhered to the lower surface of the PLC by a silk printing process.